CONFIG_IRQ_TIME_ACCOUNTING adds ns granularity irq time on each CPU.This info is already used in scheduler to do proper task chargeback(earlier patches). This patch retro-fits this ns granularityhardirq and softirq information to /proc/stat irq and softirq fields.

The update is still done on timer tick, where we look at accumulatedns hardirq/softirq time and account the tick to user/system/irq/hardirq/guestaccordingly.

No new interface added.

Earlier versions looked at adding this as new fields in some /procfiles. This one seems to be the best in terms of impact to existingapps, even though it has somewhat more kernel code than earlier versions.